copy-file: Add functions for copying non-confidential files.
Reported by Patrice Dumas <pertusus@free.fr> in
<https://lists.gnu.org/archive/html/bug-gnulib/2024-08/msg00142.html>.
* lib/copy-file.h (copy_file_to, xcopy_file_to): New declarations.
* lib/copy-file.c (copy_file_internal): New function, extracted from
qcopy_file_preserving.
(qcopy_file_preserving): Invoke it.
(copy_file_to): New function.
(handle_error_code): New function, extracted from xcopy_file_preserving.
(xcopy_file_preserving): Invoke it.
(xcopy_file_to): New function.